SQL Delete

In contrast to other commonly used statements that return, add, or modify data, the SQL DELETE statement removes records from a table, provided the user has permissions to do so.

As such, unlike using a simple SELECT statement or other queries, the SQL DELETE statement should be used with considerable caution as its execution removes data from a database and is not reversible.

A SQL DELETE statement in its simplest form would be as below:

DELETE FROM <table>;

This statement would delete all records in a table, leaving the table empty. Instead, a SQL DELETE statement is almost always combined with a WHERE clause specifying which data to delete based upon a condition or conditions that the rows must satisfy. In this case, a SQL DELETE statement would take the general form:

DELETE FROM <table> WHERE <condition>;

For example, if we wanted to delete all rows in the employees table where the gender of the employee is male, we could do so using the statement as below:

DELETE FROM employees WHERE gender = 'M';

As with UPDATE and INSERT statements, a SQL DELETE statement will not return any data upon completion, only whether it was successful or unsuccessful in execution. 

The DELETE statement is useful for arranging data in ad hoc working tables but would likely not be required by a Data Analyst or Data Scientist working in a relational database otherwise; for a data engineer its usage might be much more common. 

It should also be noted that in most organizations, the ability to execute a SQL DELETE statement would likely be restricted to privileged users, given the potential for data loss.